I'd go with the classic 1922 Cartier mounting for your Asscher cut diamond.
I've lost all my photos in a computer crash, however, I'm thinking of the integrated basket head/shank with 5 stones on each side of the shank and little 'v's engraved on each side of the end of the diamonds on the shank. Not like the BTD version with the prong head.
Keep it simple would be my motto for this center stone. It must 'shine'!
I can't wait to see what you do with this stone! Whatever you choose is going to be magnificent! You have amazing taste...
OH! I just found the perfect example for you of the 1922 Cartier Asscher ring I was thinking of: Cartier 1922